> is in many ways tantamount to destroying that evidence.
Nope. Doesn't fly. You imply that now that person can be jailed and held in contempt indefinitely until they comply.
Ok, so what if they forgot the password? What then? Forgetting the password is not the same as physically taking a hammer and destroying the hard drive. As far as the prosecution getting access to the documents, it has the same effect, but that is just that -- the same effect, it does not fall into the "knowingly destroying evidence" type action automatically.
So now you suggest that basically people can punished for forgetting. I see a big problem with that.
Moreover you give a (wrong) password and it doesn't work. You say "I am pretty sure that was right, to the best of my knowledge. I suppose I could have gotten it wrong, or maybe even the drive is damaged....." How do they know that this is a deliberate act? It seems here that lying to the police suddenly gives some degree of protection which strikes me as somewhat insane.
Indeed there have been cases in the UK where the defendant's apparent cooperation was enough to ensure there could be no RIPA prosecution even though the password to the encrypted hard drive did not seem to work. So this is not merely hypothetical.